FRAZIER MOORE

There was scant evidence suggesting it would be a hit. In October 2000 a quirky drama called CSI: Crime Scene Investigation was a last-minute addition to the US television schedules that told a story through stray hair fibres and blood spatter patterns.

But in the 15 years since it first aired, CSI has become a smash hit first in the United States and then around the globe. For several years it was the most-watched television show in the world.

This week the popular series – which has spawned three spin-offs and is credited with making forensic science sexy – comes to an end with a two-hour farewell episode broadcast in the US tonight and on Tuesday in the UK.

“I figured there would be an audience for it among those people who do crossword puzzles,” said William Petersen, the show’s original star. “I never thought the audience would also be everyone who’s never done a crossword puzzle.”

Petersen left after eight series of playing forensics lab boss Gil Grissom, but will return in the finale.

Set in Las Vegas, CSI occupies the world of forensic investigators who solve criminal cases not in the streets or an interrogation room, but in the laboratory, where the truth reveals itself from the evidence.

The two-hour farewell brings back bygone stars including Marg Helgenberger (who played blood-spatter expert Catherine Willows until departing three seasons ago) and Petersen.

Petersen said he was looking for a TV series in 2000, “but I didn’t want to play a lawyer, a cop or a divorced dad. CSI was something different, and while we didn’t know what it was going to be, we wanted a chance to figure it out.”

But why was CSI so big, for so long? “What our show did was give you the truth,” Petersen said. “You can be confused about many things, but this little piece of lint that we found on the floor, you can count on that. Granted, it was just one small truth about one particular case, but it was something you could touch and see and trust in.”

“The show had a new way of coming at crime and murder and mayhem,” said Ted Danson, who joined in season 12 as new boss DB Russell. “Taking a scientific point of view on a crime show was new back then, and allowed viewers into the darker side of life in a way that wasn’t just cops-and-robbers.”

Helgenberger said: “On pretty much every show we got the guy, thanks to irrefutable science. We made science fun and interesting.”

As Grissom told his colleagues on an early episode: forget personalities, ambitions and assumptions and “concentrate on what cannot lie: the evidence”. Ever since on CSI, hard evidence paved the way to enlightenment.

The trip ends this week, “by offering the fans an opportunity to say goodbye to the people they fell in love with at the start,” said Danson, who added: “It will be very satisfying.”

“I still feel a little delirious,” said Jorja Fox, who played forensic investigator Sara Sidle. “I feel like, wow, look at this amazing run we were able to have! And now we’ve gotten a chance to close the book. That’s a comforting feeling.”